A Highly Sensitive and Compact Size Microstrip Sensor for Characterization of Solid and Liquid Material With Broad Range Permittivity

In this work, a small planar microwave sensor based on a band-stop filter is proposed for measuring the relative permittivity of the materials. The operation frequency of the presented sensor is 2.24 GHz. It is composed of a microstrip line and an M-shaped slot as the host and sensing area respectively. This structure has been fabricated with printed circuit board (PCB) technology on the RO4003c. The sensing performance has been verified through the fabrication and measurement of a prototype to characterize the solid and the liquid samples. The correlation between the resonance frequency and relative permittivity is almost linear. The resonant frequency variation of the proposed sensor (2.24 GHz to 1.97 GHz) is proportional to dielectric constant of samples under test which is in a wide from 2.43 to 80 This sensor illustrates superior performances in comparison with similar structures in the fields of broad-range permittivity for Material under test (MUT) and the size of the transducer. The experimental results for solid-liquid materials indicate that the normalized sensitivity is 1.43% - 0.95% which is better than most similar structures. The size of the proto-type sensor (7mm $\times 14$ mm $\times 0.508$ mm) is smaller than those reported in the literature.